1. Technical Field
The present invention relates to an organic electroluminescent device and a display device.
2. Related Art
Electroluminescent devices, selfluminous all-solid-state devices that are more visible and resistant to shock, are expected to find wider application.
Researches on electroluminescent devices by using organic compounds started with a single crystal for example of anthracene, but single crystals, which were larger in thickness at a film thickness of approximately 1 mm, demanded a high driving voltage of 100 V or more.
Recently, research and development on such laminated EL devices have been in progress intensively.
Such a laminated-film device gives high-brightness emission, while positive holes and electrons are injected from electrodes through a charge-transporting layer of a charge-transporting organic compound into an emitting layer of a fluorescent organic compound and the positive holes and electrons injected and trapped into the light-emitting layer recombined to each other while the carrier balance between the positive hole and the electron is maintained.
Display devices using an organic electroluminescent device are more suited for reduction in size and thickness than other display devices such as liquid crystal, and would be used more widely in portable devices driven by an internal power supply. It is important to make the device operate for a longer period with lower power consumption for use in such a portable device.
On the other hand, organic electroluminescent devices commonly have a basic layer structure composed of an ITO transparent electrode (anode), a positive hole-transporting layer (or light-emitting layer having a charge-transporting potential) provided thereon, and other layers provided as needed. For use in the applications described above and for energy conservation, known is a method of providing a buffer layer between the transparent electrode and the positive hole-transporting layer (or light-emitting layer having a charge-transporting potential) and thus, improving the charge (positive hole) injection efficiency into the positive hole-transporting layer (or light-emitting layer having a charge-transporting potential), and it is possible to reduce the driving voltage by the method. Examples of the materials for the buffer layer include PEDOT (polyethylene-dioxythiophene), star-burst amines, CuPc (copper phthalocyanine), and the like.